JP4509825B2 - Mobile communication system - Google Patents

Description

  The present invention relates to a mobile communication system used for communication in a mobile body such as a train or a car, and more specifically, mobile that performs communication based on network mobility in a heterogeneous composite communication system in which a narrowband communication area and a broadband communication area are mixed. The present invention relates to a body communication system.

  In a conventional train radio system, a digitization system using a leaky coaxial cable radio (LCX) is often used for the radio I / F. LCX has a smaller communication band than the current broadband environment and is generally difficult to use as a line for Internet access, and is used exclusively for business radio.

  On the other hand, large-capacity communication infrastructures such as wireless LANs and millimeter-wave wireless systems have been established, and experiments for applying these to train systems and the like are being conducted.

  In the case of a wireless LAN, the communication band is secured about 10 Mbps (IEEE802.11b) to 54 Mbps (IEEE802.11a, g) and can be used as an interface for Internet access, but it is covered by one wireless base station. Since the area that can be produced is small, the time that can be communicated from a train moving at high speed to one radio base station is short. For this reason, even when radio base stations are continuously arranged with high density, there is a problem that radio base station handovers (HO) frequently occur.

  In the case of a millimeter-wave wireless system, a communication band of about several Mbps to several tens of Mbps is secured, and it can be used as an Internet access interface like a wireless LAN. Since the area that can be used is small, the time that can be communicated from a high-speed moving train to one radio base station is short, and even when radio base stations are continuously arranged at high density, frequent handovers (H .O) occurs.

  In the train radio system, apart from the existing communication infrastructure that can always be connected by leaky coaxial cable radio, a broadband communication infrastructure such as a new wireless LAN, millimeter wave radio system, etc. should be arranged on the track so that it can always be connected. Wireless access that can accommodate high-speed movement in a narrow band, such as placing narrow-band communication infrastructure and broadband communication infrastructure by dividing areas, or placing broadband communication infrastructure in spots near stations, etc. Thus, a service using a complex environment of different types of wireless communication that realizes communication by combining with wireless access that is intermittently arranged in the network becomes a practical method.

  Patent Documents 1 and 2 are conventional techniques related to such a heterogeneous composite wireless system. In Patent Document 1, high-speed and narrow-band radio is used in a high-speed and narrow-band radio communication area in a complex radio environment having low-speed and wide-band radio (cellular) and high-speed and narrow-band radio (wireless LAN). However, when outside the high-speed / narrow-band radio communication area and within the low-speed / wide-band radio communication area, the low-speed / wide-band radio is used for communication. By assigning channels to a plurality of channels, it seems that a high-speed and wide-area wireless network exists.

  Patent Document 2 has two wireless communication systems, and when performing handover between two wireless systems, it communicates with the HO destination wireless system via the wireless system connected in advance and enters the handover destination system. Information (various communication service information such as requested service, transmission band, MAC address and ID after H.O, encryption key, etc.) is obtained.

Japanese translation of PCT publication No. 2003-510897 JP 2003-235064 A

  When a heterogeneous radio system is applied to the train radio system and the Internet is always connected, when only a low-rate leaky coaxial cable radio is always connected, an access speed of only about several tens of kbps can be obtained. Users cannot use it at the same time. Also, when a narrowband leaky coaxial cable radio is used in combination with a wideband wireless LAN or millimeter-wave radio system, TCP / IP communication can be used immediately at high speed when handing over from a narrowband radio to a wideband radio. This is not possible with a normal switch, and the transfer rate gradually increases after handover is completed.

  As described above, when realizing a heterogeneous wireless system using both a narrowband wireless system and a broadband wireless system, the conventional technique increases the transfer rate for a while after handover from the narrowband wireless area to the broadband wireless area. Therefore, there arises a problem that the broadband wireless section cannot be used efficiently. This problem is further inefficient when broadband wireless sections are scattered in spots.

  The present invention has been made in view of the above, and uses a broadband wireless section efficiently by increasing the transfer rate immediately after the handover from the narrowband wireless section to the broadband wireless section is completed. An object of the present invention is to obtain a mobile communication system.

  In order to solve the above-described problems and achieve the object, the present invention provides a mobile router having a plurality of terminals under its control and a narrowband communication area continuously along the moving path of the moving object. A plurality of narrowband radio base stations arranged so as to be obtained, and a plurality of wideband radio base stations arranged so as to obtain an intermittent wideband communication area. In a mobile communication system comprising a home agent connected to a network and performing communication based on network mobility, a handover prior to detecting a time immediately before a handover from a narrowband communication area to a wideband communication area based on the position of the mobile body The mobile router includes a detection device, and the mobile router distributes based on the detection signal of the handover pre-detection device. A response signal for communication data from the terminal of the terminal in a pseudo manner and a spoofing process for terminating the response signal from the communication partner of the subordinate terminal and a buffer for outputting the communication data from the subordinate terminal after buffering The home agent includes a first spoofing / buffering unit that executes ring processing, and the home agent returns a response signal for the communication data from the communication partner to the communication partner in a pseudo manner based on a detection signal of the handover pre-detection device. And a second spoofing / buffering unit for executing a spoofing process for terminating a response signal from the terminal and a buffering process for buffering and outputting communication data from the communication partner. .

  According to the present invention, the TCP spoofing / buffering function is executed in the mobile router and the home agent immediately before the handover from the narrowband communication area to the broadband communication area. As a result, it is possible to immediately increase the transfer rate to the wideband wireless transfer rate level, thereby achieving an effect of efficiently performing communication via the wideband wireless area.

  Embodiments of a mobile communication system according to the present invention will be described below in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.

Embodiment 1 FIG.
FIG. 1 is a diagram showing a system configuration of a first embodiment of a mobile communication system according to the present invention. The mobile communication system shown in FIG. 1 basically operates based on Mobile IP network mobility (NEMO) technology. As is well known, in mobile IP, each terminal performs movement detection / location registration, whereas in NEMO, a mobile router (MR) in a moving network (mobile network) detects movement / location in units of mobile networks. Perform registration.

  In the mobile communication system shown in FIG. 1, a train 50 as a mobile unit includes a mobile router (MR) 9 and information terminals (mobile nodes: MN) 10a, 10b,. A wireless adapter 6 for narrowband wireless (for example, leaky coaxial cable wireless) connected to the router 9 and a wireless adapter 7 for broadband wireless (for example, wireless LAN, millimeter wave wireless system) connected to the mobile router 9 A train position detecting device 11 for measuring the train position is provided. The train position detection device 11 detects the train position based on information such as position detection information by GPS, the speed of the train, the ID of the connected narrowband radio base station, and the current position based on the train position information. The time required to enter the broadband wireless communication area is accurately calculated.

  A plurality of narrowband wireless networks are continuously arranged along the travel route of the train 50. Reference numerals 5a to 5c denote wireless base stations of each narrowband wireless network. A broadband wireless network is intermittently arranged as a spot area. Reference numeral 8 denotes a wireless base station of the broadband wireless network.

  The radio base stations 5a to 5c of the narrowband radio network are connected to an access router 2a that accommodates these radio base stations 5a to 5c. The wireless base station 8 of the broadband wireless network is connected to the access router 2b. The home agent (HA) 1 manages the correspondence between the home address on the home network where the MR 9 originally exists and a plurality of temporary addresses at the handover destination for each MR, and when the MR 9 leaves the home network Has a role to transfer packets to the MR 9 using an IP tunnel. The HA 1 is connected to the core IP network 3. 4 is a web server as a communication partner node (CN) on the Internet, and the web server 4 transmits content data to the request source by TCP in response to an HTTP request.

  FIG. 2 shows a protocol stack configuration of MR9. The MR 9 has a TCP stack 100, a network mobility (NEMO) compatible mobile IP stack 101, an IP stack 102, an Ethernet MAC layer 103 for trains, and a MAC layer 104 for narrowband radio as protocol stack configurations. And a MAC layer 105 for broadband wireless communication. The TCP stack 100 has a TCP spoofing / buffer function unit 106.

  FIG. 3 shows the protocol stack configuration of HA1. The HA 1 has a TCP stack 120, a network mobility (NEMO) compatible mobile IP stack 121, an IP stack 122, an Ethernet MAC layer 123 for the core IP network 3, and an Ethernet MAC layer for the mobile network as protocol stack configurations. 124. The TCP stack 120 has a TCP spoofing / buffer function unit 126.

  Next, the operation of the mobile communication system will be described with reference to the sequence diagram shown in FIG. 4, the flowchart shown in FIG. 4 shows a mobile terminal (MN) 10a, a mobile router (MR) 9, a wireless adapter (RF # 1) 6 for narrowband wireless, a wireless adapter (RF # 2) 7 for broadband wireless, and a narrowband wireless network. A radio base station (BS # 1) 5, a radio base station (BS # 2) 8 of a broadband radio network, an access router (AR # 1) 2a that accommodates a narrowband radio base station 5, and a broadband radio base station 8 FIG. 6 is a sequence diagram illustrating a signal flow among an access router (AR # 2) 2b, a home agent (HA) 1, and a web server (CN) 4. FIG. 5 shows an operation procedure of TCP spoofing / buffering at the time of handover (HO) performed by the mobile router (MR) 9.

  In the case of normal communication in which the train is in the area of the narrowband wireless network, when the information terminal 10a that has completed location registration in the train accesses the web server 4 on the IP network 3, the information from the information terminal 10a The IP data is converted into an IP tunnel by using the reverse tunnel ring function in the mobile router 9, and then transmitted to the home agent 1 via the narrowband wireless adapter 6, the narrowband wireless base station 5, and the access router 2a. The home agent 1 extracts IP data from the mobile IP tunnel and transmits it to the web server 4. On the other hand, IP data from the web server 4 to the mobile router 9 is intercepted by the home agent 1, IPinIP-encapsulated, and transferred to the mobile router 9. The mobile router 9 performs decapsulation after reception and transfers it to the subordinate information terminal 10a.

  At the time of these data transmissions, in the case of web access, since TCP is used as a protocol, ACK as a response signal is returned to the information terminal 10 along the original route. Depending on the contents of the TCP window control and flow control, basically, the next TCP data is transmitted to the web server 4 by returning the ACK. In FIG. 2, this data flow is indicated by reference numeral 40.

  At this time, since communication is performed via narrowband wireless, the bandwidth is limited. Therefore, information terminal 10 on the train communicates with TCP data at a low rate according to the transmission rate of narrowband wireless. Become. Similarly, TCP data from the web server 4 is also communicated at a low rate in accordance with the transmission rate of the narrowband radio. The train position detection device 11 mounted on the train always detects the position of the train, and uses the detected train position, the train speed, the position information of the broadband wireless communication area stored in advance, and the like. The time required to enter the broadband wireless communication area from the present time is calculated. The train position detection device 11 sends a handover pre-detection message as shown in FIG. 6 to the mobile router 9 when the calculated intrusion time to the broadband wireless communication area reaches a predetermined time set in advance. Is transmitted (FIG. 5, step S100).

  As shown in FIG. The O pre-detection message is a message code 140 indicating that it is a handover pre-detection message, the current train position information 141, The time required until O is configured.

  H. The mobile router 9 that has received the O pre-detection message searches the database in the mobile router using the train position information 141 as a key, and extracts the transmission rate information of the broadband wireless area to enter from now on (step S110). In the database, a transmission rate as transmission band information is registered and stored for each broadband wireless area. Further, the mobile router 9 calculates the time when the IP data can be buffered from the transmission rate, the transmission rate of the narrowband radio currently used, and the memory size secured by the mobile router 9, and the buffering TCP spoofing that replies a response signal ACK to the communication request (TCP data) transmitted from the subordinate information terminal 10 from the time when the possible time is reached, and terminates reception of the ACK signal from the web server 4 side Then, data buffering for buffering a communication request (TCP data) from the information terminal 10 is started (step S120).

  On the other hand, the mobile router 9 receives the H.264 signal from the train position detection device 11. When the O pre-detection message is received, the home agent 1 receives the H.264 message as shown in FIG. O Send a pre-detection message. As shown in FIG. The O pre-detection message includes a message code 150 indicating that it is a handover pre-detection message, transmission rate information 151 of the broadband radio area of the handover destination, and changed window size information 152. The window size information 152 refers to the size of data that can be received at one time by the sliding window method. The pre-detection message includes the window size information set larger than that in the narrowband communication, and is sent to the home agent 1 in advance of the handover to prepare for broadband communication in advance (step S120). ).

  This H. The O pre-detection message includes a wireless adapter (RF # 1) 6 for narrowband wireless, a wireless base station (BS # 1) 5 of a narrowband wireless network, and an access router (AR # 1) that accommodates the narrowband wireless base station 5 ) It is transferred to the home agent (HA) 1 via 2a. This H. Triggered by the reception of the O pre-detection message, the home agent 1 artificially returns a response signal ACK to the communication request (TCP data) transmitted from the web server 4 to the web server 4 and from the information terminal 10a side. TCP spoofing for terminating reception of the ACK signal and data buffering for buffering a communication request (TCP data) from the web server 4 are started. Further, the home agent 1 greatly changes the window size of data to be sent to the mobile router 9 based on the received window size information 152.

  First, in the TCP spoofing process performed by the mobile router 9, when TCP spoofing is started, the mobile router 9 virtually returns an ACK for the TCP data from the information terminal 10a to the information terminal 10. As a reply cycle of this ACK, a pseudo response is made at a response speed according to the wireless connection of the broadband wireless network to be handed over from now on. When the mobile router 9 receives the ACK signal actually transmitted from the web server 4 side, the mobile router 9 terminates the ACK signal without sending the ACK signal to the subordinate information terminal 10a.

  Thus, since the mobile router 9 makes a pseudo response to ACK at a response speed according to the wireless connection of the broadband wireless network, the transmission interval of the TCP data from the information terminal 10 to the mobile router 9 becomes short, The data rate between the information terminal 10 and the mobile router 9 gradually increases. However, at this point, since the wireless layer still uses narrowband wireless, the actual transmission rate has not increased, and the transfer rate between the information terminal 10 and the mobile router 9 and the narrowband wireless network The data corresponding to the difference from the transfer rate is stored by the data buffering process in the mobile router 9.

  The same applies to the home agent 1, and the response signal ACK is artificially sent back to the web server 4 at a response speed according to the wireless connection of the broadband wireless network, whereby the transfer rate between the home agent 1 and the web server 4. Thus, the data corresponding to the difference between the transfer rate in the narrowband wireless network is stored by the data buffering process in the home agent 1. Further, data sent from the home agent 1 to the mobile router 9 is terminated at the mobile router 9 as a result, but the window size is large.

  When the train enters the broadband wireless area, the H.O request 34 is transmitted from the broadband wireless adapter (RF # 2) 7 to the mobile router 9 (step S130). The mobile router 9 performs mobile IP processing such as location registration update processing for the home agent 1 to switch the transmission destination from the narrowband wireless adapter 6 to the broadband wireless adapter 7. Then, the mobile router 9 sequentially transmits the buffered data to the home agent 1 via broadband wireless. Note that the TCP spoofing function and the buffer function described above are operated until the buffer becomes empty. When the buffer becomes empty (step S140), the mobile router 9 turns off the TCP spoofing function and the buffering function, and returns the processing to the normal operation (step S150). The flow of traffic returning to normal operation is shown as 41 in FIG.

  As described above, on the protocol stack in the mobile router 9 shown in FIG. 2, the data entered from the Ethernet MAC layer 103 for the train passes through the TCP spoofing / buffering 106 when the TCP spoofing function is ON. Then, the packet enters the TCP 100, and is transmitted to the wireless layer via the mobile IP stack 101 through the MAC layer 104 for narrowband wireless or the MAC layer 105 for broadband wireless. The TCP pseudo ACK is transmitted from the TCP spoofing 106 through the IP layer 102 to the Ethernet MAC layer 103 for in-train use.

  On the other hand, the home agent 1 detects that the mobile router 9 has entered the broadband wireless area by the location registration update process. Using this detection as a trigger, the home agent 1 sequentially transmits the buffered data to the mobile router 9 via the broadband wireless area with the previously changed window size. Note that the TCP spoofing function and the buffer function described above are operated until the buffer becomes empty. When the buffer becomes empty, the home agent 1 turns off the TCP spoofing function and the buffering function, and returns the processing to the normal operation.

  As described above, on the protocol stack of the home agent 1 shown in FIG. 4, the data entered from the Ethernet MAC layer 123 for the core IP network 3 has the TCP spoofing / buffering 126 when the TCP spoofing function is ON. It passes through the TCP 120 and is transmitted through the mobile network stack 121 via the mobile IP stack 121. The TCP pseudo ACK is transmitted from the TCP spoofing 126 to the Ethernet MAC layer 123 for the core IP network 3 through the IP layer 122.

  Next, a change in the data rate at the time of HO from narrowband wireless communication to wideband wireless communication due to the presence or absence of the TCP spoofing + buffering function will be described with reference to FIG. In FIG. 8, a solid line indicates a case where the TCP spoofing + buffering function is provided, and a broken line indicates a case where the same function is not provided.

  In the case of the prior art having no TCP spoofing / buffering function indicated by a broken line in FIG. After the completion of O, the transfer rate gradually increases. On the other hand, when the TCP spoofing / buffering function is ON, a pseudo ACK is transmitted from the time when HO is detected in advance, and TCP data is buffered. Immediately after completion of O, the data rate has increased to the broadband wireless transfer rate level.

  As described above, in the first embodiment, the TCP spoofing / buffering function is executed in the mobile router 9 and the home agent 1 from the prior point of the handover from the narrowband communication area to the wideband communication area, and the window is displayed in advance. Since the size is also increased, it is possible to immediately increase the transfer rate to the broadband wireless transfer rate level when the above handover is completed. Thus, it is possible to efficiently perform communication via a broadband wireless area from a moving body moving on the network.

  Further, the transmission rate information of the broadband communication area to be handed over is obtained based on the detected position of the mobile body, the transmission rate information, the transmission rate of the currently used narrowband radio, and the memory secured by the mobile router The time for which communication data can be buffered is calculated from the size, and the TCP spoofing / buffering function is executed when the bufferable time is reached, so TCP spoofing is performed for an appropriate time according to the buffer size. / The buffering function can be executed.

  In the above description, the window size change notification is sent from the mobile router 9 to the home agent 1. However, the window size change notification is also sent from the home agent 1 to the mobile router 9, You may make it change a window size by weight.

Embodiment 2. FIG.
Next, a second embodiment of the present invention will be described with reference to FIGS. FIG. 9 is a system configuration diagram of the mobile communication system according to the second embodiment. The system configuration is substantially the same as the system configuration diagram according to the first embodiment shown in FIG. A train position management server 12 is arranged on the IP network instead of the detection device 11. FIG. 10 is a sequence diagram illustrating a signal flow of the system according to the second embodiment. In the case of FIG. 10, the train position management server (P-SV) 12 is configured to transmit the above-described prior position detection message to the home agent 1 and the mobile router 9.

  In the system of the second embodiment, the train location management server 12 on the IP network always grasps train location information from the location registration operation of the mobile router 9 by the home agent 1. That is, the train location management server 12 acquires location registration information of the mobile router 9 from the home agent 1. When the train position management server 12 detects that the train has entered the position immediately before the handover to the broadband wireless communication area in the narrowband wireless area, the train position management server 12 searches the internal database and transmits the transmission rate information of the broadband wireless area that will enter from now on. Take out. In the database in the train position management server 12, a transmission rate as transmission band information is registered and stored for each broadband wireless area.

  Then, the train location management server 12 obtains IP data from the transmission rate, the transmission rate of the currently used narrowband radio, and the memory size reserved by the home agent 1 and mobile router 9 stored in advance. The bufferable time is calculated, and when the bufferable time is reached, the home agent 1 and the mobile router 9 are connected to the H.264 as shown in FIG. O Send a pre-detection message.

  These H.P. The home agent 1 and the mobile router 9 that have received the O pre-detection message start TCP spoofing and data buffering as in the first embodiment. In this way, in the home agent 1, uplink data from the information terminal 10 is buffered, and in the home agent 1, downlink data from the web server 4 is buffered. When the train enters the broadband wireless area, the mobile router 9 sequentially transmits the buffered data to the home agent 1 via the broadband wireless as in the first embodiment. The buffered data is sequentially transmitted to the mobile router 9 via the broadband wireless area. Such an operation and the TCP spoofing function are executed until the buffer becomes empty. When the buffer becomes empty, the mobile router 9 and the home agent 1 turn off the TCP spoofing function and the buffering function and perform processing. Return to normal operation.

  As described above, in the second embodiment, the handover pre-detection device is present as the train position management server 12 on the external network, and the train position management server 12 detects the mobile object detected from the position registration operation of the home agent 1. The transmission rate information of the broadband communication area to be handed over is determined based on the position of the mobile station, and communication data is obtained from the transmission rate information, the transmission rate of the currently used narrowband radio, and the memory size secured by the mobile router. The bufferable time is calculated, and the detection signal is output when the bufferable time is reached. Also in the second embodiment, the TCP spoofing / buffering function is executed in the mobile router 9 and the home agent 1 from the prior point of the handover from the narrowband communication area to the wideband communication area, and the window size is increased in advance. As a result, it is possible to immediately increase the transfer rate to the broadband wireless transmission rate level when the handover is completed, thereby moving the broadband wireless area at high speed even in a narrow section. It is possible to efficiently perform communication from a mobile body via a broadband wireless area.

  As described above, the mobile communication system according to the present invention is useful for a system that performs communication in a mobile body such as a train or a car based on network mobility in a heterogeneous composite communication system in which a narrowband communication area and a broadband communication area are mixed. It is.

1 is a diagram showing a mobile communication system according to a first embodiment. It is a figure which shows the protocol stack of a mobile router. It is a figure which shows the protocol stack of a home agent. FIG. 2 is a sequence diagram showing a signal flow of the mobile communication system according to the first embodiment. It is a flowchart which shows the TCP spoofing and buffering operation | movement in a mobile router. It is a figure which shows the format of the hand-over prior detection message which a mobile body position detection apparatus outputs to a mobile router. It is a figure which shows the format of the hand-over prior detection message which a mobile router outputs to a home agent. 6 is a diagram showing a change in transmission rate before and after a handover according to Embodiment 1. FIG. FIG. 3 is a diagram showing a mobile communication system according to a second embodiment. FIG. 5 is a sequence diagram showing a signal flow of the mobile communication system according to the second embodiment.

Explanation of symbols

1 Home Agent (HA)
2a, 2b Access router 3 Network 4 Web server 5a-5c Narrowband wireless base station 6 Narrowband wireless adapter 6 Narrowband wireless adapter 7 Broadband wireless adapter 8 Broadband wireless base station 9 Mobile router (MR)
10, 10a, 10b Information terminal 11 Train position detection device 12 Train position management server 50 Train (moving body)

Claims (5)

A mobile router mounted on a mobile unit and having a plurality of terminals under the mobile unit, a plurality of narrowband radio base stations arranged so that a narrowband communication area can be continuously obtained along the moving path of the mobile unit, and intermittent Communication based on network mobility, comprising a plurality of broadband wireless base stations arranged to obtain a general broadband communication area, a home agent connected to an external network, and mobile router movement detection / location registration In a mobile communication system to perform,
A handover pre-detection device that detects a point in time immediately before a handover from a narrowband communication area to a broadband communication area based on a mobile object position;
The mobile router
Based on the detection signal of the handover pre-detection device, a spoofing process for pseudo return of a response signal to communication data from a subordinate terminal to the terminal and termination of a response signal from a communication partner of the subordinate terminal and the subordinate terminal A first spoofing / buffering unit that executes a buffering process for buffering communication data from
With
The home agent, based on the detection signal of the handover pre-detection device, spoofing processing that returns a response signal to the communication data from the communication partner to the communication partner and terminates the response signal from the terminal; A second spoofing / buffering unit that executes a buffering process for buffering communication data from a communication partner and outputting the buffered data;
A mobile communication system comprising:   The mobile communication according to claim 1, wherein the first and second spoofing / buffering units terminate the spoofing process and the buffering process as soon as the buffered data disappears after the handover is completed. system.   3. The first and second spoofing / buffering units execute a pseudo reply of the response signal with a response speed according to a connection to a broadband communication area to be handed over. The mobile communication system described. The handover pre-detection device is mounted on a mobile object,
The mobile router obtains transmission rate information of a broadband communication area to be handed over based on reception of a detection signal of the handover pre-detection device, and transmits the transmission rate information, a transmission rate of a currently used narrowband radio, The time for which communication data can be buffered is calculated from the memory size secured by the router, and when the bufferable time is reached, the response signal is returned to the communication partner in a pseudo manner, and the spoofing process and the buffer are performed. Perform the ring process ,
Further, the mobile router transmits a detection signal of the handover pre-detection device including transmission rate information of a broadband communication area to be handed over to the home agent based on reception of the detection signal of the handover pre-detection device. The mobile communication system according to any one of claims 1 to 3. The handover pre-detection device exists on the external network,
Obtaining transmission rate information of a broadband communication area to be handed over based on the position of the mobile body detected from the location registration operation of the home agent, the transmission rate information, the transmission rate of the currently used narrowband radio, and the mobile router 4. The communication data buffering time is calculated from the memory size secured by the first and second detection signals are output when the buffering time is reached. The mobile communication system according to one.

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